Western Scrub-Jay, a common and widespread species of oak woodlands and scrub habitats within the Pacific slope of the U.S., and uncommon in open oak-juniper woodlands in the interior West, was poorly represented in the 1992-2006 MAPS database with 237 adult individuals banded and only 26 between-year recaptures of adults recorded at 47 stations located in 7 Bird Conservation Regions (BCRs).  As shown in the spatial display of results, the largest numbers of adults (about 57% of the total) were banded in Coastal California (BCR 32), with the next largest numbers of adults (21%) being banded in the Northern Pacific Rainforest (BCR 5); only 52 adults were banded within the range of the interior subspecies.

Temporal and spatial analyses of 1992-2006 program-wide MAPS data showed weighted mean population density indices for Western Scrub-Jay of 0.6 and 1.1 adults per station, respectively, from the selected models.  These densities, like those for the other three jay species included on this website, were low, only about 20% and 30% as high, respectively, as the analogous mean density indices for all species on the website.  These low indices likely reflect the difficulty of capturing these relatively large-bodied birds in the fine mesh mist nets employed in the MAPS program, but may also reflect a relatively low actual density of birds, especially among populations in the interior West.  Annual variability in population density (42.1%) was high about 80% higher than the analogous mean variability for all species, while spatial variability in population density (8.1%) was, perhaps surprisingly, about 80% lower than the analogous mean variability for all species.  The linear time model for the index of adult population density produced a significantly negative Beta of -0.055 adults per station per year, suggesting a decreasing population for Western Scrub-Jay.

The weighted geometric means of the model-averaged annual and BCR-specific lambda estimates (0.958 and 0.962, respectively, neither of which was significantly different from 1.0) suggested a non-significantly decreasing population for Western Scrub-Jay, which agreed with the decreasing index of population density suggested above.  It also agreed with as the population trend from the 1992-2006 program-wide North American Breeding Bird Survey (BBS; a lambda of 0.993 that was not significantly different than 1.0) that also indicated a non-significantly decreasing population.  The annual variability of lambda for Western Scrub-Jay (23.6%) was very similar to the analogous mean variability for all species (23.0%), while spatial variability of lambda (7.9%) was rather high, about 44% higher than the analogous mean variability for all species (5.5%).

Temporal and spatial analyses produced model-averaged estimates for adult apparent survival for Western Scrub-Jay (0.589 and 0.605, respectively) that were about as expected, considering the body mass of the species (the fourth heaviest of the 158 species on the website) as compared to the body masses of all other 157 species.  These estimates, however, were the lowest of the four species of jays included on this website, and thus were somewhat deficient and, perhaps, one cause of the apparently declining overall population of this species.  Because of the very low number of between-year recaptures of adults, however, usable annual and BCR-specific estimates of adult apparent survival could only be obtained for 7 years and 4 BCRs, respectively.  Perhaps because of this, both annual and spatial variabilities in adult apparent survival for Western Scrub-Jay (44.1% and 24.5%, respectively) were rather high, about 86% and 57% higher, respectively, than the analogous mean variabilities for all species.

Temporal and spatial analyses produced mean estimates of the productivity index for Western Scrub-Jay that were identical to each other (0.611 from the selected models) and were substantially higher than the analogous mean estimates for all species on the website (0.384 and 0.383, respectively).  They also were the second highest of the four jay species included on the website, being only slightly lower than those for Gray Jay.  Thus, overall productivity for Western Scrub-Jay was likely not deficient.  Annual variability in productivity for Western Scrub-Jay (63.7%), like annual variability in adult apparent survival, was high, about 50% higher than the analogous mean variability for all species, but spatial variability in productivity (44.2%) was about 7% lower than the analogous mean variability for all species.

Temporal analyses among Western Scrub-Jay vital rates showed that lambda was strongly and nearly significantly positively correlated with productivity, moderately but not significantly positively correlated with post-breeding effects, and weakly and non-significantly negatively correlated with adult apparent survival.  These results suggest that annual variation in lambda was driven by annual variation in productivity and, to a lesser extent, by annual variation in post-breeding effects.  In addition, post-breeding effects were moderately but not significantly negatively correlated with both adult apparent survival and productivity, while adult apparent survival was also moderately but not significantly negatively correlated with productivity.  These results suggest possible competitive interactions both among and between adult and young birds that could have affected the both the true survival of adult and young birds throughout the year, as well as the emigration/immigration of adults and the recruitment of surviving young during the subsequent breeding season.

Temporal analyses also showed that lambda was moderately but not significantly negatively correlated with the index of adult population density, suggesting that the population dynamics of Western Scrub-Jay were likely effected, at least to some extent, in a density-dependent manner.  In addition, productivity was also moderately but not significantly negatively correlated with population density; post-breeding effects were very weakly (if at all) negatively correlated with population density; and adult apparent survival was rather strongly but non-significantly positively correlated with population density.  These results suggest that density-dependence in Western Scrub-Jay was brought about virtually entirely through productivity.  These results also indicate that the vital rate whose annual variations were the major driver of annual variation in lambda (productivity) was the same vital rate through which density dependence was primarily effected, a relatively uncommon situation among the landbird species included on this website, but possibly more common among permanent resident species, such as Western Scrub-Jay, than among migratory species.

Spatial analyses showed that lambda was very strongly and significantly positively correlated with adult apparent survival, weakly and non-significantly negatively correlated with productivity, and essentially not correlated at all with post-breeding effects.  These results suggest that spatial variation in lambda was driven virtually entirely by spatial variation in adult apparent survival.  Post-breeding effects were also very strongly and very nearly significantly negatively correlated with productivity, and moderately but not significantly negatively correlated with adult apparent survival, again suggesting likely competitive interactions both among young birds and between young and adult birds.  This competition likely affected both the survival of young birds during the non-breeding season and the recruitment of surviving young during the subsequent breeding season.  As perhaps expected from these latter two correlations, adult apparent survival was rather weakly and non-significantly positively correlated with productivity.

Summary of research and management hypotheses – Although Western Scrub-Jay is widely distributed across its range in the West, and common at least within the Pacific slope portion of its range, the population declines indicated by both MAPS and the BBS suggest that research and management efforts to reverse the declines and maintain stable populations may be warranted.  Because of the possibly deficient overall adult apparent survival for Western Scrub-Jay, and the very strong and significant spatial correlation between adult apparent survival and lambda, we suggest that research and management first be directed toward determining and managing for habitat and environmental characteristics that promote higher levels of adult survival, especially within regions where adult apparent survival is low and appears to drive population declines, which appear to be especially severe for the interior subspecies in the Southern Rockies/Colorado Plateau and the Great Basin.  Second, because annual variation in productivity appears to be the strongest driver of annual variation in lambda, even though overall productivity does not appear to be deficient, we suggest that research and management be directed toward determining and managing for habitat and environmental characteristics that promote higher levels of productivity, especially during years when productivity is low and appears to be a driver of population declines.  In addition, we suggest that research and management be directed toward determining and managing for habitat and environmental characteristics that promote higher levels of first-year survival and/or recruitment of young birds, especially during years when first-year survival and/or recruitment of young birds is low and appears to be a driver of population declines.  Finally, because productivity and survival of both adult and young birds are likely to be strongly affected by weather conditions, and because those weather conditions are likely to be strongly affected by climate change, we suggest that the research and management efforts outlined above should include considerations of both weather and climate change.

Please cite this narrative as:  DeSante, D. F., D. R. Kaschube, and J. F. Saracco.  2015.  Vital Rates of North American Landbirds.  www.VitalRatesOfNorthAmericanLandbirds.org: The Institute for Bird Populations.